143SRPP Stream Revitalization: Principles & Practices

LECTURE 2 Fluvial Geomorphology

Fluvial Systems: Watersheds, Hierarchical Structure, Morphological Forms, and Scale Characteristics and Classifications

Winter 2019 Semester 30 September 2019 Fluvial Geomorphology

Fluvial Geomorphology is the study of landforms and the processes that shape them by the transport of water and sediment through a drainage network. River Mechanics is the branch of fluvial geomorphology that quantifies the relationship between process and form in rivers and streams. Relationships are developed through a combination of field observations, physical experiments, and numerical modeling. Fluvial Geomorphology

Fluvial Geomorphology is the study of landforms and the processes that shape them by the transport of water and sediment through a fluvial system.

Fluvial forms: structural patterns of landforms at various spatial scales, from watersheds to channel bedforms.

Fluvial processes: the action when a hydraulic force from moving water induces a landform change by transporting sediment (erosional degradation) and/or lack of force causing sediment deposition (aggradation).

Hydraulic forces are dependent on flow, slope, landform\channel roughness (flow resistance) influencing local degradation and aggradation.

Classic Reference: Knighton, D. 1998. Fluvial Forms and Processes: A New Perspective. Taylor and Francis Group, London. 383 p. Fluvial Systems: Dominant Controls

Knighton (1998) Fluvial Systems: Dominant Controls

Fluvial System landforms are dependent on dominant upstream and/or downstream controls.

Fluvial Processes

Vertical adjustment processes: knickpoint migration Schumm (1977, 2005) Fluvial Systems: Dominant Upstream Controls

The naming of a lithology is based on the rock type: three major types: sedimentary, igneous, and metamorphic.

Lithology may be either a detailed description of these characteristics or be a summary of the gross physical character of a rock.

Other definitions

Alluvial deposition zones occur at breaks from mountainous regions into valleys and tributary junctions.

Piedmont is a landform created at the foot of a mountain or mountains by debris deposited by shifting streams.

Landforms / Geological Controls New Mexico, USA (Ritter 1986) Knighton (1998) Fluvial Systems: Dominant Upstream Controls

Geology: Tectonics (relief) and Lithology Source: Czech Geological Survey 1:500,000 scale Fluvial Systems: Dominant Upstream Controls

Geology: Tectonics (relief) and Lithology Source: Czech Geological Survey 1:50,000 scale

Praha

Vitkov Fluvial Systems: Dominant Upstream Controls

Geology: Tectonics (relief) and Lithology -- State of Tennessee, USA Fluvial Systems: Dominant Upstream Controls

Geology: Tectonics (relief) and Lithology -- State of Tennessee, USA

West TN - Quaternary Mid TN - Ordovician

East TN - Precambrian Hydrologic Systems: Climate and Hydrology Dominant Upstream Controls: A Review

Hydrologic System A hydrologic system is defined as a “structure” in space with a boundary, that accepts a “working medium” -- water and other inputs (air, heat energy, organic matter, chemical ions) operating internally on them to produce transformed outputs.

Rainfall water Spatial and temporally distributed on the structure Stream Watershed, drainage basin, catchment outlet discharge Interactions, processes with water to produce stream flow; retention/detention soil moisture storage; evaporation, transpiration by vegetation ……. Hydrologic Systems: Climate and Hydrology Dominant Upstream Controls: A Review

Distribution of precipitation input in the water budget

Rainfall-Runoff Relationships

Viessman & Lewis (2003) Hydrologic Systems: Hydrology and Land Use Dominant Upstream Controls – A Review

Runoff Concepts: Stream Hydrographs Headwater vs downstream hydrographs

baseflow

Urban vs forested watershed hydrographs Wards and Trimble (2003) Fluvial Systems: Dominant Controls

• Watersheds are the fundamental spatial unit in fluvial geomorphology • Drainage network patterns reflect form and process relationships.

Geomorphic character is dependent on: Geology (valley shape, bank/bed material, knickpoints), watershed and riparian vegetation, channel slope, hydrology (climate), sediment supply and size, watershed position (stream order).

Fluvial Processes: Force vs Resistance Erosion vs Deposition Beaver Creek, Knox County, Mill Run Section Fluvial Systems: Watersheds

Watersheds: …..the fundamental unit A watershed is a topographic area that collects water, sediment and organic matter, and discharges of stream flow with transported materials through an outlet or mouth.

Headwaters provide largest Headwaters surface area for a drainage Drainage network network’s supply of water, sediment, and organic matter.

Mays (2005): Fig 7.1.4 Mouth Fluvial Systems: Watersheds

The watershed, the functional unit of all hydrologic and geomorphic analyses.

Watershed geomorphology refers to the physical characteristics of the watershed.

Common measures for watersheds ≤ HUC8 Watershed Characteristics: 1. Drainage Area 2. Length (longest flow path) 3. Slope (elevation difference of flow path) 4. Shape Knighton (1998) 5. Drainage density (stream length / area ) Fluvial Systems: Watersheds

Watersheds are organized as a nested hierarchy, as each small watersheds sets inside a larger one, and it sets inside a larger one and so on …….

Used by the US Geological Survey: Hydrological Unit Codes (HUC) watershed/stream identification numbers [http://nwis.waterdata.usgs.gov/tutorial/huc_def.html]

2-digit HUC first-level (region) 4-digit HUC second-level (subregion) 6-digit HUC third-level (accounting unit) 8-digit HUC fourth-level (cataloguing unit) 10-digit HUC fifth-level (watershed) 12-digit HUC sixth-level (subwatershed)

Mays (2005): Fig 7.1.5 Fluvial Systems: Spatial Scales

Fluvial Systems can consider landforms at different spatial scales with the largest scale starting with form the watershed/drainage network, and hierarchically reducing in scale to a segment/valley scale and/or reach channel/planform, bar unit (pool-riffle-bar elements), bedforms, and then to the channel processes bed sediment particle.

~ hierarchically nested

Schumm 1977, 2005; Frothingham et al. 2002 Fluvial Systems: Spatial Scales

Fluvial Spatial Scaled and Process Timescales: Timescales of various channel form components Note: Segment scale not well defined but related to spatial reflects timescale of profile gradient scale of fluvial processes and form adjustment:

Knighton (1998) Drainage Network: Longitudinal Profile

Examples Watershed Longitudinal Profile

Elevation vs Distance headwaters 0 m  downstream to mouth

Concave Upward Shape ~ a function of discharge and sediment transport (increase)

Bed Sediment ~ bed material size decreases in downstream direction; abrasion and selective sorting of sediment

Knighton (1998) Drainage Network: Longitudinal Profile

Profile concavity: influence of hardpoints and lithology  Profiles more concave bed material decreases in size downstream  Profiles less concave bed material remains constant in size downstream

Knighton (1998) Drainage Network: Longitudinal Profile

geologic knickpoints

Drift Creek, Oregon Longitudinal Profile: Channel Gradient

Concave upward shape quantified by logarithmic profile:

Hack stream-gradient index: k = (H1 - H2)/(ln L2 - ln L1)

H1 , H2 ; upstream (up/s) and downstream (d/s) elevations, respectively L1 , L2 ; up/s & d/s distances from headwaters datum 0 distance, respectively

Solid line: logarithmic profile Dashed line: river profile

Hack (1973) Drainage Network: Longitudinal Profile

Hack Stream-gradient Index

Drift Creek, Oregon canyon-section, increased slope Stream Power

Stream Power is the potential energy drop is equal to the work done to the bed and banks. All of the potential energy lost as the water flows downstream must be used up in friction or work against the bed: none can be added to kinetic energy.

Stream Power = Ώ = (γQS) (specific weight * gravity * discharge * slope)

Unit Stream Power per channel width, where b is the width of the channel. Unit Stream Power = ω = (γQS)/b

Unit Stream Power = ω = τ0V (τ0 = boundary shear stress, V = velocity)

τ0 = γRhS, where Rh is the hydraulic radius = A/P (area/wetted perimeter) Cross-sectional Area (A) = bd; where d = flow depth; Q = V/A, and assumes P = b for wide and shallow Drainage Network: Longitudinal Profile - Stream Power

Stream Power = energy (force x length) per unit time

Stream Power is a function of discharge and slope, thus a function of watershed position; Stream Power = Ώ = (gQS) (fluid density * gravity * discharge * slope)

Drift Creek, Oregon Stream Power Index = c.Ώ/w A “c” coefficient multiplied by stream power per unit channel width, with drainage area replacing Q as a surrogate for discharge. Longitudinal Profile: Geomorphic Process Continuum

Process Domain Concept

Geomorphic processes change from headwaters to large river corridors.

Processes are also hierarchical structured from watershed scale to stream bed scale.

Geomorphic analog to the River Continuum Concept.

Montgomery (1999) Fluvial Systems: Classification

Fluvial Geomorphic Classification is the categorization and description of the nature, origin and development of watershed and river landforms.

The fundamental framework of classification is that a geomorphic unit can be classified based collectively on: [DM Haskins, 1998; USFS]

1) its origin and development (process); 2) its general structure and shape (form); 3) measurements of its dimensions and characteristics (morphology); 4) the presence and status of observing morphological adjustments (geomorphic generation).

Geomorphic classification systems: form-based vs process-based, – sometimes difficult to separate.

Lecture 2 focuses on form characteristics and classification Watershed / Drainage Network Classification

Classification of watersheds / drainage networks includes: 1) drainage network patterns a function of geology 2) A classification system to denote river/stream size 3) Valley types based on geology/climate.

Segments are not well defined in the literature but have been related to stream power between major tributary junctions, or at major lithological slope knickpoints along the longitudinal profile.

Reflecting on the concept Geomorphic Process Domain, within different Valley Types, different floodplain forms and processes occur. Note: we will revisit floodplain forms and processes in Lecture 4 Drainage Network Classification

Knighton (1998) Drainage Network Classification

Structure Characteristics:

Stream Order (Strahler 1952) st nd rd th 1 , 2 , 3 , 4 ….

Drainage Density Dd = L/Ad Drainage Network Classification: Valley Types

Valley Classification: examples from Rosgen (1996)

Steep Colluvial Moderate-steep Colluvial Inner Gorge Bedrock

Glacial Trough Alluvial Terraced Alluvial Glacial Outwash

Valley quantified (Rosgen 1996) per Entrenchment Ratio is a measure of vertical containment described as the ratio of the flood-prone area width to bankfull width. Reach-scale Channel Patterns: Planform Classification

Planforms: Straight, Meandering, Braided, & Anastomosed

(Thorne et al. 1997) Planforms

Reach-scale Channel Patterns:

Classic descriptive types/characteristics

after Brice 1975 (Thorne et al. 1997) Reach-scale Channel Patterns

Channel Pattern Types: Measurement of reach-scale sinuosity Sinuosity = channel length / valley length

General patterns and relative character of channel sinuosity:

FISRWIG (1998) Reach-scale Channel Patterns: Planforms

Channel Pattern Types: Geomorphic classification, classic descriptions

after Brice 1975 (Thorne et al. 1997) Reach-scale Channel Patterns

Meander Geometry

(Thorne et al. 1997) Reach-scale Channel Patterns: Planforms

Planform type relative to: 1) sediment transport load, 2) width-depth ratio, and 3) channel stability.

(Schumm 1977) Reach-scale Channel Patterns: Planforms

Leopold and Wolman (1957) Reach-scale Channel Patterns: Planforms

Slope-discharge relationships to planform types

Note the importance of discharge (velocity), slope, bed material type, and channel cross-sectional form (Width/Depth ratio) (Knighton 1996)

Froude No., Fr = V/(gD)0.5 Ratio of inertia forces to gravitational forces

Reach-scale Channel Patterns

Flow depth (d) to grain size (D) ratio: characterizing form types

A. Robert (2003) 1 < d/D < 10

d/D > 10

d/D < 0.1

Related to channel slope and boundary resistance Reach-scale Channel Classification

Reach-scale Channel Classification has been used to aid stream restoration design by using analog or reference stream measurements.

Classifications systems vary with level of process-based morphological concepts --- it has been argued process determines form so all channel classification schemes represent process-form types.

Three Common Channel Classification Schemes: ■ Rosgen (Natural Channel Design) Classification ■ Buffington and Montgomery (Sediment Transport/Supply) Classification ■ Downs (Morphological Change) Classification Reach-scale Channel Classification

Rosgen System of Stream Classification

Based on: 1. slope 2. sinuosity 3. Width/depth ratio 4. Entrenchment ratio 5. bed sediment

Defines: Stream types A, B, C, D, DA, E, F,G (Rosgen 1996) Reach-scale Channel Classification

Rosgen System of Stream Classification

Based on: 1. slope 2. sinuosity 3. W/D ratio 4. entrenchment 5. bed sediment

(Rosgen 1996) Reach-scale Channel Classification

Rosgen System of Stream Classification

(Rosgen 1996) Reach-scale Channel Classification

Rosgen System of Stream Classification

(Rosgen 1996) Geomorphic Classification of Channel Reaches

Buffington and Montgomery (1997) Transport-limited streams are with sediment loads that exceed hydraulic capacity, and hence deposition may be prevalent.

Supply-limited streams have hydraulic capacity beyond supply, and hence scour and erosion may be prevalent.

The steeper channels (step-pool, cascade, and possibly bedrock) transmit high sediment loads and maintain their morphology, while flatter channels (braided, regime, riffle-pool) experience morphological adjustment with increased sediment.

Geomorphic Classification of Channel Reaches

Downs (1995) system based on trends and types of morphological change:

Stable Depositional Lateral Migration Enlarging Compound Recovering Undercutting

(Thorne et al. 1997) Channel Unit / Bedform Scale

Bar Unit: A hydraulic morphological unit consisting of a pool, riffle, and bar. Riffle-Pool and Step-Pool Sequences: A longitudinal profile through the channel thalweg examining riffle-pool or step pool sequences. Pool: A relatively deep location in the channel with tranquil water surface during baseflows. Riffle: A relatively shallow location with fast moving water, turbulent water as observed during baseflows. Bar: A relatively shallow location in the channel from sediment deposition (e.g., point bar). Thalweg: The corridor (pathway) longitudinally through channel with the deepest water depth.

Bedform Configuration: Gravel-bed Rivers

Riffle-Pool Sequence: The development of alternating deeps (pools) and shallows (riffles) is characteristic of both straight and meandering channels with heterogeneous bed materials, containing gravel, in the size range of 2 to 256 mm.

In general, riffle-pool sequences occur with bed slopes < 2%, and step-pool sequences occur with bed slopes > 5%.

Riffle-Pool Step-Pool

Knighton (1998) Bedform Configuration: Riffle-pool Sequences

Riffle-Pool Spacing: Average 5-7 channel unit widths from a range of 1.5 to 23.3 channel unit widths.

Knighton (1998) Bedform- Planforms Relationships

Pool-riffle sequences

Relationships with straight-meandering planforms: sinuosity and flow patterns

(Chorley et al. 1984) Bedform Configuration – Gravel-bed Rivers

Pools, riffles, and point bars are elements of a morphological structure known as a bar unit (Thompson 1986, Dietrich 1987).

Straight channel: alternative bar

Meandering channel: point bar

Braided channel: mid-channel bar (multiple bar units - not shown)

Frothingham & Rhoads (2002) Bedform Configuration: Sand-bed Rivers

Sand Bedforms: defined as irregularities in an alluvial channel bed with respect to a flat bed that are higher than the sediment size itself.

Common Types: Ripple Dune Anti-dune Chute / Bars

(Strum 2001) Bedform Configuration: Sand-bed Rivers

(Knighton 1998) Bedform Configuration: Sand-bed Rivers

Identifying bedforms as a function of flow and sediment properties:

Simons & Richardson (1966) plots stream . power (0 V) versus sediment size.

Note: . 2 (0 V) in ft-lb/s/ft

Strum (2001) Bed Sediment Particles

Bed Sediment Characterization Particle Size Classes:

Size classification as defined by the American Geophysical Union.

Each size class representing a geometric series, in which the maximum and minimum sizes differ by a factor of 2.

Diameter designated as either ds or D, depending on text source.

D50 = median particle diameter from sample/survey

Sturm (2001) Bed Sediment Particles

Bed Sediment Characterization Wolman Pebble Count: Multiple field methods to collect 100 sediment samples to perform statistics to obtain D50 or other percentile: Uniform grid, cross-sections, zig-zag pattern along the channel, and random- walk end-of-toe approach. Measure particles along the (B) intermediate axis.

Wolman (1954) Bed Sedimet Particles

Particle (Grain) Size Distribution d50 = median particle size Wolman Pebble Count: dg = geometric mean size Common Collection method g = geometric standard deviation of mixed sediment loads.

1/ 2 d d  d  84.1 g  84.1   g      d g d15.9  d15.9 

1/ 2 d g  d84.1d15.1 

Sturm (2001)